1. Field of Invention
This invention is an improved engine induction one-way valve to control intake mass flow in primarily two-stroke cycle engines. In one embodiment of this invention, a reed embodiment, the moveable sealing member is a reed; in another embodiment, a poppet embodiment, it is a spring-loaded curved plate. The moveable sealing member is bent against a curved seat preferably being a segment of an ellipse and having a relatively small average radius of curvature. The convex side of this curve always faces the incoming flow to the engine thereby presenting an aerodynamic surface for this flow; the concave side always faces the engine to minimize backflow. In order to minimize the pop-off pressure of this valve which would normally be associated with bending to this small radius of curvature, the moveable sealing member is made from a material which stress relieves and takes a set when exposed to a process which usually includes elevated temperature.
2. Description of Prior Art
Induction valves have been used extensively to control mass (air and sometimes fuel) flow into an engine, primarily two-stroke cycle engines. These two-stroke cycle engines are normally crankcase-scavenged wherein the reciprocating motion of the piston in the cylinder changes the effective crankcase volume, thus causing a pumping action. When the cylinder piston rises in its cylinder, effective crankcase volume increases creating a vacuum which causes a mass flow into the crankcase; the descending motion of the piston on the power stroke decreases crankcase volume causing an increase in crankcase pressure, this increase being used to force mass into the engine cylinder for combustion. This increase in crankcase pressure also tends to force mass flow out of the crankcase through the induction tract through which it just entered, this reverse mass flow being called backflow, reversion, or blowback. It is desirable to minimize this backflow for engine power, emissions, and fuel economy considerations.
Several methods of controlling this reverse flow have been employed; one method uses a reed valve placed in the induction tract. The reed valve design which has gained wide acceptance for crankcase-scavenged two-stroke cycle engines uses reeds firmly clamped to a reed cage, the reeds and reed cage looking much like a pup tent with the apex of the tent facing the engine. FIG. 1 of applicant""s co-pending application 09/812337 shows a commonly used reed assembly. The included angle of a reed valve is defined herein as the angle between two lines tangent to the reed ends when in the closed position. This angle by choice will be 180 degrees or less. Typically, this included angle in a conventional reed valve is in a range of 60 to 120 degrees, with the open side of the included angle facing away from the engine (toward the throttle) and its apex pointing toward the engine. Therefore, in the case of a conventional reed valve, the included angle is the angle between the two panels of the xe2x80x9ctentxe2x80x9d with the floor of the tent being on the side away from the engine and the peak of the tent pointing toward the engine.
The reed cage contains usually three or four openings in each side of the xe2x80x9ctentxe2x80x9d with reed petals which rest against seats formed into the tent, thereby closing the valve. The reed petals bend away from the seats to open the valve upon application of an opening pressure. The seats are normally flat and therefore the reeds in the closed position resting against the seats are flat. The reed petals are usually made from stainless steel, fiberglass, or carbon fiber, the latter being most widely used today. A guard plate is used in clamping the reeds to the reed cage, this guard plate limiting the maximum bending of the reed to help prevent reed damage.
Observation of open carburetors on operating engines using conventional reeds shows considerable blowback at almost all throttle positions and conditions of engine loading. This prompted this action to develop an improved induction valve which would reduce this blowback.
Several modifications in the basic design of these reed valves have been developed. U.S. Pat. No. 4,076,047 to Akahori (1978) describes using a reed petal seat which causes a slight bend in the reed in its closed position, thus creating a pre-load in the reed which aids in sealing. This pre-load in bending, however, causes an increase in the reed pop-off pressure, the pressure which must be applied to the reed to initiate an opening movement. For best operation of a reed valve in admitting mass flow into the engine with minimal entropy increase, it is desirable that this pop-off pressure be minimized. Therefore, in U.S. Pat. No. 4,076,047, an angle between the reed seat and its clamping surface in the range of 1 degree to 3 degrees is described as preferable, this small angle being a compromise between improved sealing and increased pop-off pressure.
Other reed assemblies, such as described in U.S. Pat. No. 2,612,882 to Kiekhaefer (1952), 3,008,459 to Kaufman (1961), and U.S. Pat. No. 4,408,579 to Kusche (1983) show reed valve assemblies for internal combustion engines which use a reed securely mounted to a reed cage or block in which the reed forms an included angle described above of 180 degrees. In other words, the reed seats are positioned such that the plane containing the seats (and the reeds in the closed position) lies essentially perpendicular to the engine induction passage. The tangent lines to the reed ends are therefore co-linear and the included angle is 180 degrees. These seats are also shown as being flat.
U.S. Pat. 5,601,112 to Sekiya et al. (1997) describes a valve which has a moveable sealing member which is flexible and spring-loaded. The open area of the valve and hence the valve flow rate for any pressure across the valve is determined by a combination of translational movement of the disc and flexing of the disc. If the flexibility of the disc material changes with temperature, the operation of the valve will not be uniform at various operating temperatures. Also a stopper is used which blocks a substantial portion of the dynamic pressure associated with a backflow from impacting the disc. Also shown is a disc which is essentially flat across most of its area when in the closed position; this flat portion is not an aerodynamic shape for forward flow and thus impedes forward flow through the valve.
Also, a flow control device called a liquid scroll diode is known in the art which uses no moving parts to provide asymmetric flow characteristics. These diodes provide a flow path which is offset in passing through a circular shaped cavity. The offset is positioned in the cavity to cause minimal flow momentum direction change in a forward direction. The position of the offset, however, together with the circular cavity, causes some backward flow to xe2x80x9cscrollxe2x80x9d around the circular cavity, ending up with a momentum which is in the opposite direction to which it started, namely against the original flow momentum direction. These scrolling vortices essentially reverse the momentum direction of a portion of the backward flow, directing this reversed momentum against the backward flow. This momentum reversal interferes severely with backward mass flow through the diode, providing the asymmetrical flow characteristic. It was felt that the principles used in these liquid scroll diodes could be applied to an engine induction valve to reduce blowback.
It is an object of this invention to provide an engine induction valve having a moveable sealing member with a curved shape having a convex side facing away from the engine at all operating conditions presenting an aerodynamic surface to incoming mass flow and the opposite concave side always facing the engine to cause a scrolling vortex action to outward flow thereby reducing blowback.
It is a further object of this invention to provide an engine induction valve with a moveable sealing member having an included angle between lines tangent to its ends in the closed position of less than 180 degrees with the angle opening facing toward the engine and its apex pointing away from the engine.
It is a further object of this invention to provide an engine induction valve having a uniform frequency response at various temperatures while using a moveable sealing member made from a material whose elastic modulus changes with temperature.
It is a further object of this invention to provide an engine induction valve having a moveable sealing member mounting which has more than one mounting point but allows volume expansion of the member in all directions.
It is a further object of this invention to provide an engine induction valve which uses a moveable sealing member which is forced to bend against a seat, thereby inducing a stress in the member, but being constructed of a material in which this stress is consequently diminished upon application of a process containing elevated temperature, for instance.
It is a further object of this invention to provide an engine induction valve which uses a moveable member to seal against a curved seat, this curved seat having a decreasing radius of curvature as the distance from a central axis of the member increases.